1. Field of the Invention
The present invention relates to a delivery system and method for delivering and deploying a stent. More specifically, the invention relates to a delivery system and method for delivering and deploying a self-expanding stent in a body lumen.
2. Description of the Related Art
Stents and delivery systems for deploying stents are a highly developed and well known field of medical technology. Stents have many well known uses and applications. A stent is a prosthesis which is generally tubular and which is expanded radially in a vessel or lumen to maintain its patency. Stents are widely used in body vessels, body canals, ducts or other body lumens.
The preferred present stent delivery apparatus and method utilizes a self-expanding stent, which is well known in the art. A well known self-expanding stent is the woven braided stent disclosed in U.S. Pat. Nos. 4,655,771 (Wallsten); 4,954,126 (Wallsten) and 5,061,275 (Wallsten), although any type of self-expanding stent may be deployed using the inventive delivery system and method. The delivery system of the present invention may also be used to deliver a balloon expanded stent and may also deliver stent grafts, which are well known in the art.
The delivery systems for stents are generally comprised of catheters with the stent axially surrounding the distal end of the catheter. It is highly desirable to keep the profile of the catheter as small as possible. Therefore, self-expanding stents are generally confined in a reduced radius for delivery to the deployment site. Once the stent is deployed the catheter is removed, leaving the stent implanted at the desired location to keep the vessel walls from closing.
A variety of techniques have been developed for holding a self-expanding stent in its reduced configuration while moving the distal end of the catheter to the deployment site. For example, in U.S. Pat. No. 4,655,771 (Wallsten), gripping members at either end of the stent hold the stent in an axially-elongated position, which causes the stent to take a reduced radius delivery configuration.
Another common technique for maintaining the self-expanding stent in a reduced radius delivery configuration is using a sheath which surrounds the stent and compresses it around the catheter. This technique is disclosed in U.S. Pat. No. 5,071,407 (Termin) and U.S. Pat. No. 5,064,435 (Porter), both of which use a silicon rubber sheath to compress the stent. A similar technique is disclosed in U.S. Pat. No. 5,026,377 (Burton) and U.S. Pat. No. 5,078,720 (Burton).
A variation on surrounding the stent with a sheath is disclosed in 4,732,152 (Wallsten); 4,848,343 (Wallsten) and 4,875,480 (Imbert), all of which disclose using a sleeve formed of a doubled-over section of membrane to compress and contain the stent.
U.S. Pat. No. 5,234,457 discloses using a sheath to surround a mesh stent of the type disclosed in U.S. Pat. No. 4,922,405. However, in this patent the sheath is not used to compress the stent, but is used to prevent fluid from accessing the stent. The stent is impregnated with a pure gelatin or other dissolvable material which, when cured, has sufficient strength to hold the stent in its reduced delivery configuration. Once the sheath is withdrawn, the stent is exposed to the body fluids which dissolve the gelatin, allowing the stent to self-expand. This reference also discloses using axial distribution of gelatins with different rates of thermal decomposition to control the physical profile of the stent as it expands. However, using an impregnated mesh stent adds several inconvenient manufacturing steps to the process of preparing the stent for implantation.
All of the methods for delivery of a stent discussed to this point involve releasing the stent starting from one end of the stent, except for Anderson 5,234,457 which can allow the stent to self-expand uniformly over its entire length. An improvement to this type of deployment is discussed in Heyn 5,201,757 which relates to medial deployment of a stent. Medial deployment of a stent releases the middle region of the stent before releasing either end of it. This tends to prevent stent movement during deployment.
All of the prior art methods of containing and deploying the self-expanding stent have several problems. First, many of the techniques require that movement of the entire sheath or exterior catheter take place to manipulate the distal end of the catheter and effect release of the stent. This can be seen in Wallsten 4,655,771 and Wallsten 4,954,126 in which tubular member 23 is moved forward from position 22 to position 30. In Termin 5,071,407 the sheath 32 is withdrawn proximally with respect to the stent. In Porter 5,064,435 the sheath 38 is withdrawn proximally with respect to the stent. Burton 5,026,377 also moves an outer sleeve backwards relative to the stent. In Wallsten 4,732,152; Wallsten 4,848,343, and Imbert 4,875,480, a hose 5 is connected to a maneuvering tube 8 which runs the length of the catheter. Finally, in Heyn, finger grip 5, connected to section 58 causes outer catheter 20 and sleeve 24 to move proximally relative to the stent.
In all of the cases discussed above, movement occurs over the entire length of the catheter between the proximal end controlled by the physician and the distal end where the stent is released. This catheter movement in the vessel creates several problems. First, catheter movement can disturb or move the introducer sheath at the wound site where the catheter is inserted into the vessel. Secondly, in tortuous anatomy the added friction caused by rubbing the outer catheter against the vessel can make deployment difficult. The translation of control movements from the proximal to the distal end is imprecise, jerky and in some instances impossible due to the increased friction caused by tortuosity. Thirdly, it can create trauma to the endothelium over the entire length of the catheter.
Another drawback to the prior art stent delivery systems discussed above is that requiring an extra sheath layer, sleeve layer or layered catheters (Heyn) increases the profile of the catheter, which is undesirable. The Heyn device described in U.S. Pat. No. 5,201,757 has a profile of 0.12 inches (3.048 mm). A reduction in profile of even 1F (French) is considered significant to those skilled in the art.
There remains a need in the art for a stent delivery system in which the catheter remains stationary in the vessel and movement is confined to the distal end of the catheter to avoid disturbing the introducer sheath, minimize trauma to the endothelium and allow for move easier and more accurate deployment in tortuous anatomy. Furthermore, there remains the need for a stent delivery catheter with a smaller profile than the prior art. There is also a need for an improved form of medial release.